In the course of processing a photographic element containing an imagewise exposed silver halide emulsion layer reduced silver can be formed either as a direct or inverse function of exposure. At the same time, at least a low level of reduced silver formation also occurs independently of imagewise exposure. The term "fog" is herein employed to indicate the density of the processed photographic element attributable to the latter, usually measured in minimum density areas. In color photography fog is typically observed as image dye density rather than directly as silver density.
Over the years a variety of differing materials have been introduced into silver halide emulsions to inhibit the formation of fog. Research Disclosure, Vol. 176, December 1978, Item 17643, Section VI, lists the more commonly employed fog inhibiting agents. Research Disclosure is published by Kenneth Mason Publications Limited; Emsworth; Hampshire P010 7DD; England. From Section VI it is apparent that useful fog inhibiting agents are highly diverse in their structural forms, ranging from halide ions (e.g. bromide salts) to inorganic metal salts to specific polymers to selected acyclic organic compounds to specific heterocycles. These useful fog inhibiting agents have been selected from among a plethora of structurally similar, but relatively ineffective compounds. Useful fog inhibiting agents have been largely identified empirically. T. H. James, The Theory of the Photographic Process, 4th Ed., Macmillan, 1977, pp. 393-399, in grouping and suggesting various performance mechanisms for fog inhibiting agents illustrates their diversity.
Gunther et al U.S. Ser. No. 660,155, filed Oct. 12, 1984, titled PHOTOGRAPHICALLY USEFUL CHALCOGENAZOLES, CHALCOGENAZOLINES, AND CHALCOGENAZOLINIUM AND CHALCOGENAZOLIUM SALTS, commonly assigned, discloses to be useful as intermediates in synthesizing the title heterocycles compounds containing a 1,2,5-oxatellurazinium ring fused with an aromatic ring. A synthetic procedure for preparing these novel intermediates is also disclosed.